DESCRIPTION (Applicant's Abstract) This is a renewal of a Harvard Medical School Training Program in Molecular Hematology. The program is designed to train graduate students, physicians and other biomedical scientists for academic careers focused on the study of the blood and its disorders. For this program, 60 distinguished faculty members have come together to serve as preceptors, for the students and postdoctoral fellow trainees. The program is organized around five major disciplines relevant to the broad field of Hematology-Erythroid Biology, Hemostasis-Vascular Biology, Hematopoiesis/Hematologic Malignancy, Immunology/Inflammation, Genetics, Molecular and Cellular Biology. The program selects the most promising candidates for training from a large pool of graduate students and postdoctoral fellows training at HMS and its affiliated hospitals. After nomination by a potential preceptor or program leader, trainee qualifications and research proposals are reviewed by a Steering Committee, with final appointments made by the program Co-Directors. The major training sites are the preceptor laboratories although trainees can participate in a large range of seminars, courses, laboratory and group meetings, poster sessions and other activities within the HMS community. Frequent interactions between the program Co- Directors, preceptors and trainees closely monitor the progress of each trainee. Each trainee is formally reviewed annually and meets with the program Co-Directors. Their progress is reviewed by the Steering Committee and reappointment is competitive and contingent on satisfactory progress. During the past two granting periods, 82 percent of the program's graduates have gone on to successful academic careers. Of these, 59 percent currently have funded basic science laboratories and 41 percent have successful clinical research programs. The current trainees and the program's graduates have written a total of 258 scientific papers; many in the highest quality peer-reviewed journals. New preceptors have been added to the program to provide additional strength and to reflect new areas of scientific importance. The renewal application requests a modest increase in the number of funded positions for pre and postdoctoral trainees, as the number of qualified applicants far exceeds the available positions in the current grant.